stress on the sediment surface, which ultimately finds its expression in the spatial arrangement of the sediment grains. After all it is this lateral inrush of fluid, which “sweeps up” the grains in the grooves and redeposits them in long parallel ridges underneath the lifting turbulences. This rhythmical process is known as burst and sweep. Mode of occurrence Parting lineation is restricted to coarse silts as well as to fine- and medium-grained sands (i. e. to grain sizes of 16 to 500 µ). The structure very rarely occurs in coarser sediments. Hydraulically it is characteristic for the lower part of the upper plane bed regime and results from fairly high current velocities of 0.6 to 1.3 meters per second. Parting lineation forms in very different depositional environments. The structure is most commonly found on the beach where it forms in flat, wet sediments due to swash. Parting lineation can also be created in dewatering tidal channels. Geological formations like for instance the Old Red Sandstone or the Buntsandstein also give proof of the shallow marine character. Parting lineation has even been described from turbidites. Yet the structure is not only restricted to the marine environment, it can also form in river sediments, especially on point bars. Parting-step lineation, which is characterized by step-like parting surfaces, has been reported by Banerjee from varves deposited in glacial lakes. Parting lineation was even artificially reproduced in hydraulic experiments. Remark: in the marine environment parting lineation doesn't have to be associated solely with the upper plane bed regime, it has been reported for instance from the erosive stoss side of ripple marks, megaripples and dunes. This implies that the structure can form already under lower current velocities. Due to its varied and rather widespread occurrence parting lineation is not a unanimous indicator for depositional environments. Theoretical considerations In order to derive an expression for the crosswise spacing of parting lineation it is useful to start with the quadratic stress law: τ = 1/8*f*ρ*Um2 The shear stress τ exerted by the current within the boundary layer is proportional to the square of the current velocity U. The Darcy-Weisbach friction coefficient f and the density of the fluid ρ are constants. Empirical studies have found a dimensionless value Z = 100 for the parallel streaks/ridges. This can be equated to: Z = 100 = ρ/η*Ut*λ where λ represents the measured spacing, Ut the shearing velocity and